Various types of timers have been proposed heretofore for use in the industrial field for various purposes, for instance, for opening a valve at a preselected time and for a preselected duration thereby to allow flow of water therethrough, for closing a switch to conduct an electric current, or for operating an ignition device. These known timers, however, require skill and experience and are so complicated and massive that they cannot be handled very conveniently; in addition, mechanical disorders are often encountered. The present invention intends to provide an easy-to-use, high-precision timer which is free from the disadvantages of conventional timers and highly flexible in use.